14 CFR § 135.443

No certificate holder may operate an aircraft after maintenance, preventive maintenance, or alterations are performed on the aircraft unless the certificate holder prepares, or causes the person with whom the certificate holder arranges for the performance of the maintenance, preventive maintenance, or alterations, to prepare—

An airworthiness release; or

An appropriate entry in the aircraft maintenance log.

The airworthiness release or log entry required by paragraph (a) of this section must—

Be prepared in accordance with the procedure in the certificate holder's manual;

Include a certification that—

The work was performed in accordance with the requirements of the certificate holder's manual;

All items required to be inspected were inspected by an authorized person who determined that the work was satisfactorily completed;

No known condition exists that would make the aircraft unairworthy; and

So far as the work performed is concerned, the aircraft is in condition for safe operation; and

Be signed by an authorized certificated mechanic or repairman, except that a certificated repairman may sign the release or entry only for the work for which that person is employed and for which that person is certificated.

Notwithstanding paragraph (b)(3) of this section, after maintenance, preventive maintenance, or alterations performed by a repair station located outside the United States , the airworthiness release or log entry required by paragraph (a) of this section may be signed by a person authorized by that repair station.

Instead of restating each of the conditions of the certification required by paragraph (b) of this section, the certificate holder may state in its manual that the signature of an authorized certificated mechanic or repairman constitutes that certification.